Method of extrusion of metals of hollow section



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METHOD OF EXTRUSION OF METALS OF HOLLOW SECTION Original Filed Oct. 18, 1962 4 Sheets-Sheet. l

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7 3% AMM L Q L. W I NW MN bim H- Cazir 11s United States Patent 3,196,659 ETHGD 0F EXTRUSION OF METALS 0F HGLLOW SECTION .l'ohn Harper Cairns, Stourton, near Leeds, England, assiguor of one-half to Yorkshire Imperial Metals Limited, Stonrton, England, a company of Great Britain Original application Oct. 18, 1962, Ser. No. 231,394, now Patent No. 3,172,536, dated Mar. 9, 1965. Divided and this application Aug. 26, 1964, Ser. No. 392,247 Claims priority, application Great Britain, Oct. 20, 1961, 37,681/ 61 2 tllaims. (Cl. 72-264) This application is a division of my co-pending patent application Serial No. 231,394 filed October 18, 196-2, now US. Patent No. 3,172,536, issued March 9, 1965 for Extrusion of Metals of Hollow Section, and it relates particularly to a method of commencing the extrusion of such sections.

Where a hollow section is to be extruded from a billet of heated metal the first stage is normally to pierce the billet by pushing the extrusion mandrel through the billet, to form the bore or tunnel, but difliculties often arise in securing the correct location of the bore or tunnel in the extrusion with respect to the exterior section. In consequence the tunnel is often incorrectly located with respect to the exterior part of the extrusion and extrusions are often regarded as insufiiciently accurate for some purposes.

Accordingly one object of the invention is to provide a method of extruding hollow sections in such a manner that the "bore or tunnel of the extrusion is accurately lo cated with respect to the external section.

Another object of the invention is to provide an improved method of piercing a billet prior to extrusion.

A further object is to provide a method of piercing a billet in which an enlarged nose is temporarily fitted to the front end of the extrusion mandrel to pierce an oversized tunnel through the billet, and the front end of the mandrel is subsequently supported through the nose while pressure is applied to force the metal thereof around the mandrel proper to form a correctly sized and located tunnel.

Still another object is to provide an improved method of extruding hollow metal sections.

In one aspect, as broadly claimed, the invention consists of a method of piercing a heated billet prior to extrusion in which a nose piece which is larger in crosssection than the mandrel is temporarily placed at the front of the mandrel, and the nose piece and mandrel are forced through the billet to pierce a tunnel or bore therethr-ough which is larger than the mandrel. After piercing is completed the mandrel is stopped with the nose piece supported in the extrusion die (in the opening of which it is a sliding fit) so that the nose piece and mandrel are correctly centered and located with respect to the die. Pressure is then applied to the billet to cause the metal thereof to flow around the mandrel and form a tunnel or bore in the billet which corresponds exactly in size and location with the mandrel. Since the mandrel is of the correct size and has been correctly located with respect to the die, the tunnel or bore must also be of the correct size and correctly located with respect to the die. The errors which normally occur in piercing are thus eliminated.

In another aspect, as broadly claimed, the invention consists of a method of commencing extrusion of a heated billet in which a nose piece which is larger in cross-section than the mandrel is temporarily placed at the front of the mandrel, and the nose piece and mandrel are torced through the billet to produce a tunnel or bore therethrough which is larger than the mandrel. After 3,195,659 Patented July 27, 1965 piercing the billet the mandrel is stopped with the nose piece supported by the extrusion die, so that the mandrel is correctly centered and aligned with respect to the die. Pressure is then applied to the billet and is maintained, so that the metal of the billet first flows closely around the mandrel to form a tunnel which corresponds in size and location exactly with the exterior of the mandrel and then flows out through the extrusion die to commence the extrusion, the leading end of the extrusion P shing the nose piece oil the mandrel.

Other objects and the particular features of the invention will appear from a study of the following description, with reference to the accompanying drawings, in which:

FIGURE 1 is a longitudinal section of a part of an extrusion press of normal type with the parts shown partway through a piercing operation;

FIGURE 2 is a longitudinal section similar toFIG- URE 1 showing the parts at the end of the piercing operation;

FIGURE 3 is a similar view of the parts just after extrusion has commenced;

FIGURE 4 is a longitudinal section similar to FIG- URE 1 with the parts modified to use the method of the invention;

FIGURE 5 is a perspective view of an enlarged mandrel nose for use in practisin the method according to the invention;

FIGURE 6 is a view similar to FIGURE 4 showing the parts of the press part-way through the piercing operation;

FIGURE 7 is a view similar to FIGURE 6 with the par-ts at the end of the piercing operation;

FIGURE 8 is a view similar to FIGURE 6 just after extrusion has commenced; and

FIGURE 9 is a diagrammatic representation of the lubricating and cooling system applied to the extrusion mandrel. Like references refer to like parts throughout the drawings.

Referring to FIGURES l, 2 and 3, certain parts of the front end of an extrusion press are shown. A billet of hot metal indicated by reference 1 is being enclosed in a liner 2 located inside a container 3. A die holder 4, mounted at the front of the liner, contains an extrusion die 5. The mandrel for piercing the billet and forming the tunnel through the extrusion during the extruding operation is shown at 7. The stem 8 at the front of the press ram carries a pressure disc 9 by which pressure is applied to the billet 1.

A common fault encountered in hollow extrusions made by known methods is that the tunnel or bore is inaccurately located with respect to the external section and it results from deflection of the extrusion mandrel during the piercing operations. Very heavy end pressure must be applied to the mandrel during the piercing operation and the mandrel may be subjected to side pressures which cause it to be deflected or sprung to one side. These side pressures may be caused by incorrect adjustment of the press, or on moving par-ts, but they also occur, for example, where the mandrel is necessarily of slender form, or the tunnel in the extrusion is of complex shape. As shown in FIGURE 1 the mandrel is gradually deflected in its passage through the billet and by the time it has completed the piercing operation its has been defiected to a substantial extent, as shown in FIGURE 2. Consequently, ath the beginning of extrusion, the wall thickness of the extruded product 10 is non-uniform, as shown in FIGURE 3, where the wall thickness of the extruded shell 10 is greater at the top than at the bottom.

FIGURE 4 illustrates an arrangement for introducing a supply of lubricant by making the mandrel 7 hollow and this is not a part of the present invention. The

method according to the invention comprises placing an over-size nose 6, shown separately in FIGURE 5, in the front end of the mandrel 7, the over-size nose having a spigot 16 which fits into a bore 12 formed in the end of the mandrel 7. The cross-section of the large portion of the mandrel nose is larger than the cross-section of the mandrel, as shown in FIGURE 4. The lubricant flows along an annular gap 11 between the billet l and the mandrel 7 and forms a lubricating layer between the outer surface of the mandrel 7 and the newly formed inner surface of the billet 1.

The grooves 14 and 15 are more clearly seen in the perspective view of the nose 6 in FIGURE 5. The nature of the lubricants used and the advantages thereof are more particularly described in the aforementioned copending patent application.

A feature of the present invention is that by placing the over-size nose 6 in the end of the mandrel 7, an oversize tunnel is produced in the billet I.

FIGURES 6, 7 and 8 illustrate how the use of the oversize mandrel nose 6 substantially eliminates tunnel eccentricity in the extruded product. The nose 6 is a sliding fit in the die at the extrusion temperature. FIGURE 6 shows the mandrel 7 part-way through the piercing operation. As in the previous case, illustrated in FIGURE 1, the mandrel 7 is deflected from the central axis of the billet 1 and the extrusion die by approximately the same amount as it passes through the billet. FIGURE 7 shows the position atthe end of the piercing operation, when the nose 6 has passed right through the billet and has been engaged in the opening of the die 5. The side pressure on the mandrel is relieved as soon as it passes out of the billet and the mandrel is correctly aligned and located with respect to the extrusion die by virtue of the engagement of the nose 6 in the die opening. The annular gap 11 formed during piercing allows the mandrel to be freely alignecLas is clearly shown in FIGURE 7, where the realigned mandrel 7 is no longer symmetrically placed within the annular gap 11. When the pressure is applied to the main ram at the end of the piercing operation the metal of the billet is'compressed by the pressure disc 9 so that it flows closely around the mandrel '7 and closes the annular gap Ill. The billet then contains a smaller tunnel which corresponds precisely with the shape of the mandrel 7, and since the latter is correctly aligned with the die 5, the tunnel in the billet is also correctly aligned with respect to the die.

FIGURE 8 shows the commencement of extrusion, which commences immediately after the metal of the billet has been closely pressed around the mandrel 7. The flow of extruded metal through the die pushes oil? the nose 6.

FIGURE 9 shows in diagrammatic form the lubricating and cooling system applied to the mandrel. Referring to this figure, the extruding press comprises'a hydraulic cylinder 17 containing a ram 18 by which the piercing and extrusion pressure is applied. Fixed to the outer end of the ram 18 is a crosshead 19 which carries a cam Ztl. Placed at appropriate intervals along the stroke of the crosshead are three limit switches, respectively 21, 22 and 23, whose plungers are actuated in turn by the cam 20 in the course of the stroke of the ram 18. The electrical control will be referred to more particularly later.

Fixed in the end of the crosshead I9 is a piercer stem 24, which carries the mandrel 7, and which contains a bore 25 containing a centrally located tube 26. The bore 25 communicates with a transverse bore having a connection 27 from which a pipe 28 leads to a first solenoid valve 29. The solenoid valve 29 is of a conventional type winding is de-energized. From the solenoid valve 29 a pipe 3!) leads to a lubricant pump 31, which needs no further description since any suitable kind of pump such as a geared pump, an impeller pump or a piston pump may be used. From the central tube 26 a transverse tube leads to a connection 32 from which a pipe 33 leads to a second solenoid valve 3'14, of the same type as the valve 29. From the second solenoid valve 34 a pipe 35 leads to a coolant pump 36, which may also be of a conventional type and requires no further description. The lubricant pump 33 draws lubricant via a pipe 37 from a lubricant tank 38, while a coolant pump 3t? draws coolant via a pipe 39 from a coolant tank 40. i

A non-return or check valve 41 is provided at the end of the, bore 25, the tube 26 passing through this valve, and at the end of the tube itself a second non-return or check valve 42 is provided. The check valve 4-1 prevents coolant under pressure from being forced into the lubricant bore 25, and the check valve 42 prevents lubricant under pressure from being forced into the coolant tube 2-6.

Returning now to the electrical circuitry, there are several ways of arranging the switching which will occur to persons skilled in the art, but one efective method is illustrated. The limit switch 21 is a changeover switch having a moving contact which, in its two positions, connects the live electric mains line 43 to one or other of two fixed contacts. It has. a spring loaded operating plunger which is engaged by the cam 2t? and each time the plunger is pressed in and released the moving contact changes from one fixed contact to the other. The limit switch 22 is of a similar type to the switch 21 insofar as its actuation is concerned, but it is a double changeover switch, that is to say, it contains two separate changeover switches both actuated by the one plunger. The limit switch 23 may be .of the same type as the limit switch 21. The two fixed contacts of the limit switch 21 are connected by lines 44 to one pair of fixed contacts in the switch 22 and the associated moving contact is connected by a line 45' to the first solenoid valve 29. The second moving contact in the switch 22 is connected to the main supply line 43 and the associated fixed contacts are connected by lines 45 to the two fixed contacts in the switch 23 whose moving contact is connected via a line 46' to the solenoid valve 34.

The circuitry described above consists of two separate two-position control circuits of well known type respectively for the first and second solenoid valves.

In operation, with the lubricant and coolant pumps running, the hydraulic ram 18 is initially in the position shown, which is a withdrawn position, and the cam 2% is in the rearward position shown with respect to the switches 21, 22 and 23. After a hot billet has been placed in the die chamber or liner 2, and the mandrel nose 6 has been placed in position in the end of the mandrel, hydraulic pressure is applied to the cylinder 17 and the ram 18 begins to. move forward, carrying the crosshead 19, the piercer stem 24- and the mandrel 7 forward. When the nose piece 6 reaches the billet at the cornmencement of the piercing operation, the cam 20 reaches the position shown dotted at 47 to engage the plunger of the switch 21 and actuate the switch. The changing over of the contacts in this switch energizes the first solenoid valve 29, which is opened so that lubricant is supplied through the pipe 28 to the bore 25, through the valve 41 and through the bore 13 in the mandrel, to provide lubrication during the piercing operation. When the piercing operation has been completed the cam 20 reaches the position shown dotted at 48 to actuate the plunger of the switch 22 and change over both sets of contacts. The change of one set of contacts breaks the supply over the line 45 and deenergizes the solenoid valve 29, which immediately closes. At the same instant, the change of the other pair of contacts energizes the second solenoid valve 34 over the line 46, so that this valve is opened and a supply of coolant flows through the pipe 33, the tube 26, the non-return valve 42 and the bore 13 to the interior of the extrusion. It will be recalled from the earlier description that when actual extrusion commences the nose piece 6 is pushed off the end of the mandrel and merely falls into a suitable receptacle, so that the coolant may flow freely through the bore 13 and thence into the bore in the extrusion to cool it. At the end of the extrusion stroke the cam reaches the position shown dotted at 49, to actuate the switch 23. The changing over of its contacts de-energizes the solenoid valve 34 so that this valve closes and cuts off the coolant supply.

Since the mandrel 7 is correctly aligned with respect to the die at the commencement of the extrusion operation, the extrusion is accurately formed and the tunnel thereof is correctly located with respect to the external section and this condition is maintained throughout the extrusion operation.

There are many purposes for which hollow extrusions are at present considered unsuitable because it is not possible to guarantee sufficiently accurate location of the tunnel with respect to the external section. The uses of the method according to the invention, by making possible the production of more accurately extrusions, makes it possible to apply extruded metal components in numerous new fields. The benefits provided by the method according to the invention are enhanced by the use of the apparatus disclosed in the said co-pending patent application and the two inventions used together provide the following advantages:

(a) Reduced frictional resistance between the mandrel and the billet during subsequent extrusion which reduces the required extrusion pressure, thus permitting more eflicient use of the press, e.g., by using larger billets or high extrusion ratios.

(b) Promotion of uniform flow of metal during extrusion which prevents the formation of extrusion defects that could otherwise occur under non-lubricated flow conditions.

(c) Reduced heat transfer from the billet to the mandrel during extrusion due to the lubricant film acting as a thermal barrier.

(d) Reduced frictional heating of the mandrel during extrusion and reduced tensile pull on the mandrel during extrusion, giving better tool life.

(e) Improved mandrel coolingthe coolant which is forced through the mandrel during the extrusion period absorbs much of the heat which is conducted to the mandrel from the hot billet, thereby preventing overheating of the mandrel.

(f) Avoidance of bore contamination by atmospheric gasesthe stream of coolant which emerges from the front end of the mandrel into the bore of the extruded product immediately vapourises and the copious quanties of vapour so formed prevent the ingress of atmospheric oxygen or nitrogen to the bore of the extruded product, and this prevents the formation of undesirable films of oxide or nitride on the bore surface.

(g) Improved product coolingthe stream of coolant which emerges from the hollow mandrel during extrusion causes the extruded product to cool more rapidly than would be the case with normal extrusion practice; this is particularly desirable for some metals and alloys.

What I claim is:

1. A method of piercing a heated billet prior to extrusion comprising the steps of temporarily placing at the front of an extruding mandrel a nose piece which is larger in cross-section than said mandrel, forcing said nose piece and mandrel through said billet to produce a tunnel therethrough which is larger than said mandrel, stopping said mandrel with said nose piece supported in an extrusion die so that said mandrel is correctly centered and located with respect to said die, and applying pressure to said billet to cause the metal thereof to flow around said mandrel to form a tunnel in said billet corresponding in size and location to said mandrel.

Z. A method of commencing extrusion of a heated oillet comprising the steps of temporarily placing at the front of an extruding mandrel a nose-piece which is larger in cross-section than said mandrel, forcing said nose piece and mandrel through said billet to produce a tunnel therethrough which is larger than said mandrel, stopping said mandrel with said nose piece supported in an extrusion die so that said mandrel is correctly centered and located with respect to said die, applying pressure to said billet to cause the metal thereof to flow around said mandrel and form a tunnel in said billet corresponding in shape, location and size with said mandrel, and continuing to apply said pressure to cause the metal of said billet to be extruded over said mandrel and through said die, the leading end of the extrusion pushing said nose piece away from said mandrel and out of said die.

References Cited by the Examiner FOREIGN PATENTS 593,621 2/34 Germany.

CHARLES W. LANHAM, Primary Examiner. 

1. A METHOD OF PIERCING A HEATED BILLET PRIOR TO EXTRUSION COMPRISING THE STEPS OF TEMPORARILY PLACING AT THE FRONT OF AN EXTRUDING MANDREL A NOSE PIECE WHICH IS LARGER IN CROSS-SECTION THAN SAID MANDREL, FORCING SAID NOSE PIECE AND MANDREL THROUGH SAID BILLET TO PRODUCE A TUNNEL THERETHROUGH WHICH IS LARGER THAN SAID MANDREL, STOPPING SAID MANDREL WITH SAID NOSE PIECE SUPPORTED IN AN EXTRUSION DIE SO THAT SAID MANDREL IS CORRECTLY CENTERED AND LOCATED WITH RESPECT TO SAID DIE, AND APPLYING PRESSURE TO SAID BILLET TO CAUSE THE METAL THEREOF TO FLOW AROUND SAID MANDREL TO FORM A TUNNEL IN SAID BILLET CORRESPONDING IN SIZE AND LOCATION TO SAID MANDREL. 